锌白铜微米掺杂对纳米导电银胶性能的影响

纳米导电银胶因其便捷的使用条件被广泛地应用于芯片封装及电子制造业中,但纳米粒子容易团聚,导致导电银胶的导电性下降。为改善纳米银粒子的分散性,首次选用微米锌白铜颗粒对纳米银片进行掺杂改性,研究了纳米导电银胶中掺杂微米锌白铜颗粒对导电银胶导电性及热性能的影响。分析了不同接触类型的导电通路对纳米导电银胶导电性的影响。实验结果表明,锌白铜颗粒的加入可以改善纳米银片在环氧体系中的分散性,改善导电银胶导电性,当锌白铜添加量占填料质量分数的4%时,导电胶的体积电阻率可达1.68×10~(-4)Ω·cm。且锌白铜的加入有利于提升导电银胶的温度稳定性。当锌白铜添加量占填料质量分数的12%时,导电胶的平均电阻温度系数为0.0045/℃。     

一种新型芯片粘接用导电银胶的性能研究

制备了一种由环氧树脂基体、咪唑类固化剂、微米级银粉和活性稀释剂体系构成的导电银胶。该导电银胶的常温体积电阻率为3.7×10~(-4)Ω·cm,搁置寿命大于48 h,粘度适中,耐热散热性能良好。将该导电银胶应用在3种引线框架并考察其可靠性,结果表明导电银胶与无镀层框架的粘接性最好,但在高温时各框架的粘接性相差不大。同时考察了该导电银胶应用于LGA封装的芯片粘接效果,封装后界面无气泡和分层现象。     

具有稳定接触电阻和卓越抗冲击性能的导电银胶

表面贴片组装导电胶（SMCAs)为电子行业的导电连接提供了一种环境友好的解决方案，而且与传统的Sn/Pb合金焊锡膏相比，SMCAs具有低温加工和更小间距组装等非常有吸引力的技术优势。然而，要作为合金焊锡膏的替代品，SMCAs尚面临着一些重大的阻碍，其中在不同温度和湿度下，导电性（接触电阻）、不稳定和胶接点抗冲击性能较差，是目前SMCAs商业化的两大致命缺陷。因此我们对为什么普通SMCAs的接触电阻不稳定和抗冲击性能较差的基本机理进行了系统研究。研究表明接触电阻稳定性主要和导电金属有关，暗示金属表面的电化学腐蚀是接触电阻不稳定的主要原因，同时，研究还解释了能量耗散是控制SMCAs连接点抗冲击或跌落测试性能的关键因素。基于以上的研究结果，我们采用新的方式开发新一代的SMCAs。这些新材料的接触电阻稳定性显著提高并具有卓越的抗冲击性能。     

导电银胶触变性的研究

以环氧树脂为基体,银粉为填料,制备出IC封装用导电银胶。研究了环氧树脂与银粉的比例、银粉的形貌和粒径以及触变剂SiO2的用量对导电银胶触变性的影响。结果表明,银胶触变性随树脂/银粉质量比的减小而增大,当其为0.2时,触变指数达到5.68。在一定粒径范围内,银胶的触变性与银粉粒径呈反比关系;银胶触变性随SiO2的用量增大而增大。     

高导热烧结银胶的可靠性研究

市场对功率半导体器件的导热和导电性能要求越来越高,经过调查评估找到了一款纳米级烧结银胶。对该纳米级烧结银胶的粘结强度、导电性、调入性和可靠性进行了研究,并与普通铅锡焊料及普通导电胶进行了对比分析,发现纳米级烧结银胶具备粘结强度超强、平均剪切强度稳定、导热导电性能高等特点,并且在经历严格的热应力和机械应力试验后,其粘结强度、导电导热性能保持稳定,没有下降的现象。因此,高导热纳米烧结银胶可作为导热性要求极高的高可靠性应用领域的一种理想材料。     

低熔点Sn-Ag-Cu合金成分的优化

发现Sn-Ag和Sn-Cu二元相图的共晶点Sn96.2Ag3.8和Sn98.7Cu1.3的平均原子尺寸相等,Ra=0.154 6nm.从而在三元Sn-Ag-Cu合金中,通过连接Sn-Ag和Sn-Cu二元共晶点得到一条Ra=0.154 6 nm的平均原子尺寸线,考虑到误差,在这条线近处选择了Ra=0.154 4和Ra=0.1548的两条平均原子尺寸线.在高真空下用电弧熔炼法制备了三类合金(Sn96.2Ag3.8)x(Sn98.7Cu1.3)1-x(x=0.1,0.3,0.5,0.7)、(Sn94Ag6)x(Sn97.8Cu2.2)1-x(x=0.2,0.5,0.7)和(Sn98Ag2)x(Sn99.3Cu0.7)1-x(x=0.1,0.3,0.6).     

钯银合金镀层性能

根据接触电阻,抗腐蚀性,耐磨性和微振磨损试验数据表明,电镀的钯银合金对于连接器来说是一种富有生命力的镀层。含40％银的钯银合金镀层比钯或者钯镍合金镀层性能好,成本低。     

无颗粒银导电墨水及高导电率银薄膜的制备及其性能研究

以酒石酸银为原料、1,2丙二胺为络合剂、无水乙醇为溶剂制备了无颗粒银基导电墨水,将该墨水棒涂于玻璃、PET、PI和相纸基板,在加热板上130℃固化5 min获得银膜,通过XRD、FTIR、TG-DSC、FE-SEM和四探针测电阻率方法对合成的酒石酸银粉体、导电墨水和银膜进行表征。结果表明:导电墨水的分解温度远低于银前驱体的分解温度;在不同基板上的银薄膜表现出不同的形貌和颗粒尺寸,其中相纸基板上的电阻率最低为6.7×10~(–6)?·cm。喷墨打印银线条于PI基板,130℃固化5 min后,银线条宽度约100μm,表面平整光滑且微观组织致密,在柔性印刷方向有良好的应用前景。     

冷却方式和应变速率对SnBi36Ag0.5合金力学性能的影响

研究了熔炼制备的SnBi36Ag0.5无铅焊料于水冷、空冷、模冷三种方式冷却后,在应变速率为0.00067,0.00167和0.00333 s^-1下的力学性能和断裂行为。利用X射线衍射仪(XRD)、光学金相显微镜(OM)、扫描电镜能谱(SEM)和万能材料试验机分别对合金的物相、显微组织、断口形貌和力学性能进行表征。结果表明,冷却速度增加使焊料脆硬富Bi相和Ag₃Sn相得到细化,析出的富Bi颗粒减少。冷却速度越大、应变速率越小,合金的抗拉强度越低,断后延伸率越高。合金断口形貌逐渐由脆性断裂变为韧脆混合型断裂,韧窝的数量和面积逐渐增大。当冷却方式为水冷,应变速率为0.00067 s^-1时,合金的延伸率有最大值78.58%,应变速率为0.00333 s^-1时延伸率也能达到55.76%,通过水冷能明显改善合金的脆性。     

银胶,金胶的结构形态和聚合特点

本文报道了用兑制的方法制备的银胶，金胶在电镜下的结构形态和聚合行为，并与表面增强拉曼散射（ＳＥＲＳ）常用的活性基底的其它银胶和金胶进行了对比。发现兑制方法制备的胶体与以往其它方法制备的胶体明显不同，兑制的银胶，金胶颗粒形成不够完善，尺度较小且大多成团状堆积；加入吡啶分子后并未像其它方法制备的银胶，金胶那样进一步凝聚，而是凝聚程度有所减弱，加入Ｃｌ＾－后，结构形态发生显著变化，原来胶体中大量的团状结     

Electrical and mechanical characterization of an anisotropic conductive adhesive with a low melting point solder

For the highly reliable interconnection in a micro-packaging technology requiring an excellent electrical and mechanical performance, the new anisotropic conductive adhesive (ACA) system with a low melting point solder was designed and characterized. An optimum flip-chip bonding cycle considering the chemo-rheological properties of a polymer matrix and solder was proposed. The bonding mechanism of the new ACA system was experimentally observed by the optical microscope. The electrical properties such as electrical resistance of about 5.6 mΩ and current density of 10,000 A/cm² were measured by the 4-point probe test. The measured shear strength was 304 MPa after bonding process.Electrical and mechanical performances were measured and compared before and after a pressure cooker test (PCT). In order to get a more stable ACA system during processing, the polymer matrix mixed with a reductant and a low melting point solder powder will be continuously developed in the near future.     

焦耳热作用下共晶锡铋焊点电迁移特性

电迁移可以引发芯片内部互连金属引线（单一元素）中的原子或离子沿电子运动方向移动. 但是,在共晶锡铋焊点中,组成的元素为锡和铋而非单一元素. 由于铋原子和锡原子在高电流密度下具有不同的迁移速率,因此共晶锡铋钎料具有独特的电迁移特性. 实验中采用的电流密度为1E4A/cm2,同时焦耳热会引发焊点温度从25升高至49℃,富铋相在此温度下会发生明显粗化,除此之外,铋原子会首先到达正极界面处并形成坚硬的阻挡层,使得锡原子的定向运动受到阻碍,最终,富锡相会凸起,其与负极界面间会有凹谷形成.     

焦耳热作用下共晶锡铋焊点电迁移特性

电迁移可以引发芯片内部互连金属引线(单一元素)中的原子或离子沿电子运动方向移动.但是,在共晶锡铋焊点中,组成的元素为锡和铋而非单一元素.由于铋原子和锡原子在高电流密度下具有不同的迁移速率,因此共晶锡铋钎料具有独特的电迁移特性.实验中采用的电流密度为104A/cm2,同时焦耳热会引发焊点温度从25升高至49℃,富铋相在此温度下会发生明显粗化,除此之外,铋原子会首先到达正极界面处并形成坚硬的阻挡层,使得锡原子的定向运动受到阻碍,最终,富锡相会,凸起,其与负极界面问会有凹谷形成.     

Chemo-rheological characteristics of a self-assembling anisotropic conductive adhesive system containing a low-melting point solder

To achieve the excellent wettability of a solder in an anisotropic conductive adhesive (ACA) in micro-packaging technology, not only the removal of the oxidized layer of the solder but also the chemo-rheological phenomena of the thermally induced self assembly of low-melting temperature solder powders were investigated for ACA applications. Both the optimum kind and amount of reductant were determined in this study to remove the oxidized layer formed on the solder surface in ambient environment. The solder wetting test was performed to observe the chemical and rheological compatibility between the solder, polymer matrix, and reductant. The thermal analysis was done using differential scanning calorimetry (DSC) analysis and rheometer test. Several chemical reactions by the reductant were proposed, and the mechanisms were postulated. It is believed that the reductant reacts with the oxidized layer, amine, and epoxide group, respectively. The relation between conversion and glass transition temperature of the polymer matrix was also obtained from DSC.     

Characterization of polymer matrix and low melting point solder for anisotropic conductive film

The chemo-rheological mechanisms of a polymer matrix and a low melting point solder for an anisotropic conductive film (ACF) have been characterized. For the material characterization of the polymer matrix and solder, a differential scanning calorimetry (DSC) and a dynamic mechanical analyzer (DMA) experiments were conducted. The conversion and viscosity of the polymer matrix was observed by DSC and DMA, respectively. In order to control the curing conditions such as the reaction temperature and time of polymer matrix, the adequate amount of catalyst was used. The compatibility between the viscosity of a polymer matrix and a melting temperature of solder was characterized to optimize the processing cycle. The reductant was also added to remove the oxide layer performed on the surface of solder in the air environment. Based on these chemo-rheological phenomena of the polymer matrix and solder, the optimum polymer system and its processing cycle were designed for the high performance and reliability in the electrical interconnection system.     

Effect of microalloying on the creep strength and microstructure of an eutectic Sn-Pb solder alloy

The present research aims to improve the creep strength of Sn-Pb eutectic solder by the addition of small amount of effective elements, such as Sb, Ag, Cu, and Ga, which are selected by preliminary experiments and analysis. Creep tests were conducted at the stress and temperature range of 5 N/m to 15 N/m m² and 313 K to 378 K, respectively. The microalloying treatment increased significantly the creep-rupture time by one order at the same condition of creep stress and temperature, comparing with that of the regular Sn-Pb eutectic solder alloy. Microstructural observation indicated that the excellent creep properties are obtained by the particles dispersion hardening due to the combined addition of the microalloying elements.     

Curing kinetics of anisotropic conductive adhesive film

Polymer-based conductive-adhesive materials have become widely used in many electronic packaging interconnect applications, such as chip-on-glass, chip-on-flex, etc. Among all the conductive-adhesive materials, anisotropic conductive adhesive film (ACF) is an attractive interconnect material because of its fine pitch capability. Anisotropic conductive-adhesive film is a thermosetting, epoxy matrix impregnated with a small amount of electrically conductive particles. During component assembly, the epoxy resin is cured to provide mechanical connection, and the conducting medium provides electrical connection in the z direction. The thermal cure process is critical to develop the ultimate electrical and mechanical properties of the ACF. In this paper, the curing reaction of ACF was studied with a differential scanning calorimeter (DSC) under isothermal conditions in the range of 120–180°C. An autocatalyzed kinetic model was used to describe the curing reaction. The rate constant and the reaction orders were determined and used to predict the progress of the curing reaction. A good agreement is found between the proposed kinetic model and the experimental reaction-rate data. The reaction-rate constants were correlated with the isothermal temperature by the Arrhenius equation. The glass-transition temperature also has been studied as a function of cure degree and moisture absorption.     

Microwave preheating of anisotropic conductive adhesive films for high-speed flip chip on flex bonding

Anisotropic conductive adhesive film (ACF) can be preheated by microwave (MW) radiation in order to reduce the bonding time for flip-chip technology. Due to sluggish and nonuniform curing kinetics at the beginning of the curing reaction, thermal curing of epoxy is more time consuming. Therefore, MW radiation may be more effective, due to its uniform heating rate during the cycle. In this paper, MW preheating (for 1–4 sec) of ACF prior to final bonding has been applied to determine the electrical and mechanical performance of the bond. Powers of 80 and 240 W MW were used to study the effect of the MW preheating. A final bonding time of 6–7 sec can be used for flip chip on flex bonding instead of 10–15 sec (standard time for flip chip bonding) for MW preheating time and power used in this study. The contact resistance (as low as 0.01) is low in these samples, whereas the standard resistance is 0.017 ohm (bonded at 180°C for 10 sec without prior MW preheating). The shear forces at breakage were satisfactory (0.167–0.183 KN) for the samples bonded for 6–7 sec with MW preheating. This is very close and even higher than the standard sample (0.173 KN). For MW preheating power of 80 W and sweeping time of 2 sec, final bonding at 6 sec can also be used because of its low contact resistance (0.019 ohm). Scanning electron microscope (SEM) investigation of microjoints and fracture surface shows uneven distribution of conductive particles and thick bond lines in samples bonded for 5 sec (with MW preheating). Samples treated with MW radiation (80 W and 2–3 sec time) serve as evidence that well-distributed particles along with thin bond lines cause low contact resistance and high joint strength.     

Effects of novel carboxylic acid-based reductants on the wetting characteristics of anisotropic conductive adhesive with low melting point alloy filler

A low viscosity epoxy resin with carboxylic acid-based novel reductants was introduced to improve the process ability and reliability of an anisotropic conductive adhesive (ACA) resin with a low melting point alloy (LMPA) filler system. The curing degree of the ACA resin and the melting of the LMPA filler were investigated using differential scanning calorimetry (DSC) conducted in the dynamic mode in order to control the curing conditions such as the reaction temperature and a melting temperature of solder. The temperature-dependent viscosity characteristics of the ACA resin were investigated using a rheometer. The compatibility between the viscosity of a polymer matrix and a melting temperature of solder was characterized to optimize the processing cycle. Three different types of carboxyl acid-based reductants were added to remove the oxide layer on the surfaces of the filler particles and the conductive pad. Good wetting properties were achieved between the LMPA filler and the Cu pad in the epoxy resin using these carboxylic acid-based reductants.     

Electrical characterization of isotropic conductive adhesive under mechanical loading

Isotropic conductive adhesive (ICA) is a strong candidate for replacing toxic lead-based solders. Before wide application of this new technology can occur, the degradation mechanisms must be thoroughly understood. In this work, we investigated the electrical characteristics of a commercial ICA under mechanical loading. The results showed that the resistance rose monotonically with the joint strain in the lap shear test, while it increased steadily with the number of cycles in the low-cycle fatigue test. To elucidate the experimental observations, two-dimensional finite-element modeling (FEM) was carried out, and the effects of mechanical loading on the initial intimate interaction among silver fillers were analyzed. Additionally, based on modeling, the possible electrical degradation mechanisms were discussed.